As the resin composition for encapsulation which is used for encapsulating photosemiconductor elements such as light emitting diodes (LED) and the like, a cured product thereof is required to have transparency. In general, epoxy resin compositions obtained by using epoxy resins such as bisphenol A-type epoxy resins, alicyclic epoxy resins or the like, and acid anhydrides as the curing agent, are commonly used.
In view of its transparency, heat resistance and light resistance, there have been proposed an epoxy resin composition obtained by employing the alicyclic epoxy resin represented by the following structural formula (b) (see Document 1) and a method of modifying the epoxy resin with silicone, decreasing the elastic modulus, and reducing the internal stress (see Document 2).

Document 1: Unexamined published Japanese patent application No. 7-309927
Document 2: Unexamined published Japanese patent application No. 7-25987